1. Field of the Invention
The invention relates to apparatus for acoustically treating sinusoidal and/or random noise as may be emitted by an internal combustion engine or other sources which emit noise through a valve port or other restricted venting or exhausting aperture, and, more particularly, to mufflers for automobiles and the like.
2. Discussion of the Prior Art
Because the majority of sound or noise supression apparatus, which may generally be referred to as mufflers, is associated with internal combustion engines, this category of application is particularly addressed. Muffler designs are generally of two basic types or configurations: (1) a compartmentalized type which comprises several compartments sealed except for the inlets and outlets, the compartments usually being sealed, noise entrapment chambers; and (2) a type commonly known as a "straight through" buffer, that comprises a perforated duct within a sealed housing. Other mufflers are generally variations of these two basic types.
The first, compartmentalized type muffler has the disadvantages of complexity, large volume requirements for expansion of the gases, and a large size to enclose the compartments. Due to their complexity, such type mufflers create a substantial pressure drop and thus exert substantial back pressure against the exhaust source, thereby reducing engine efficiency. The second straight through -type muffler, although of less complex structure and producing lower back pressure than the first mentioned type, does not provide sufficient noise suppression to be generally acceptable.
A further disadvantage of heretofore known muffler configurations has been the inability to economically manufacture such mufflers so that they will withstand the corrosive road salt (calcium chloride) placed on icy roads in the winter; known muffler housings quickly corrode through from repeated exposure to such salt.